1. Field of the Invention
The present invention relates to an absorbent article for pantiliners, sanitary napkins, incontinence pads, diapers, etc., more particularly, to such an absorbent article having a water-decomposable backsheet.
2. Description of the Related Art
Recently, the absorbent articles such as the pantiliners and sanitary napkins disposable in flush toilets have come available. For example, Japanese Unexamined Patent Publication (Kokai) Nos. Heisei 8-38547 and 8-19571 disclose water-decomposable absorbent articles comprising a water-decomposable absorbent core and water-decomposable topsheet and backsheet between which the absorbent core is sandwiched.
The water-decomposable absorbent articles such as pantiliners and sanitary napkins have respectively an adhesive layer formed on the rear surface of the backsheet for fitting the absorbent article to an external support such as an undergarment. After used, the absorbent articles are peeled from external supports at the adhesive layer, and disposed of in flush toilets.
These water-decomposable absorbent articles are composed of constituent components (absorbent core, topsheet, backsheet, etc.) having increased decomposability in water. However, the conventional water-decomposable components of such absorbent articles are generally problematic in that, when their decomposability in water is increased, the bonding strength of fibers constituting them tends to be inevitably lowered in wet and dry condition. Therefore, it is difficult to increase both the decomposability in water and the strength of the water-decomposable components of absorbent articles.
In pantiliners and sanitary napkins having an adhesive layer on the backsheet for fitting them to external supports, when the backsheet is made from a water-decomposable material, the bonding strength between the backsheet and the adhesive layer is lowered. As a result, when the absorbent articles are, after used, peeled from external supports, the adhesive layer is often peeled from the backsheet to remain on external supports, and, in addition, the fibers constituting the backsheet may adhere to and remain on external supports along with the adhesive layer.
In such pantiliners and sanitary napkins, if the strength of the backsheet is low, it will cause another problem in that, when the basic weight (Metsuke) of the backsheet is reduced and the thickness thereof is reduced, the backsheet will lose the function of retaining the shape of the absorbent articles while they are worn, so that the absorbent articles may be deformed or distorted.
An object of the present invention is to provide an absorbent article of which the backsheet is decomposable in water and satisfies the two requirements of high decomposability in water and good surface strength enough for use.
According to an aspect of the invention, an absorbent article may comprise a backsheet, a liquid-pervious topsheet and a water-decomposable absorbent core sandwiched between the backsheet and the topsheet, at least the backsheet being made from a water-decomposable material, wherein;
the backsheet is formed of a fibrous sheet that contains water-dispersible fibers and water-insoluble carboxymethyl cellulose, and
the water-insoluble carboxymethyl cellulose has a degree of etherification (D.S.) falling between 0.3 and 0.6, and is modified so that the hydrogens of at least 95% of carboxylic acids therein are substituted with metal.
In the absorbent article of the invention, the backsheet is formed of a fibrous sheet of which the surface strength and the breaking strength in the direction of the thickness are both high. Therefore, the backsheet surely retains the shape thereof during being used. Furthermore, when the absorbent article is, after used, peeled from an external support at the adhesive layer formed on the rear surface of the backsheet, the backsheet is not separated from the adhesive layer so that the backsheet hardly remains on the external support fitting with the adhesive layer. The breaking strength in the direction of the thickness of the backsheet is meant to indicate the breaking resistance of a fibrous sheet forming the backsheet in the direction of the thickness, when a tensile force is applied to the sheet in the vertically opposite directions so as to separate the front surface from the rear surface thereof.
For example, the metal is at least one selected from the group consisting of calcium, sodium, magnesium, zinc, manganese, lithium, barium, and aluminium.
In case where an adhesive layer for securing the absorbent article to an external support is formed on the rear side of the backsheet, the present invention produces better results.
The basic weight of the fibrous sheet to form the backsheet falls, for example, between 10 and 50 g/m2.
Preferably, the water-insoluble carboxymethyl cellulose accounts for from 1 to 30% by weight of the fibrous sheet to form the backsheet.
Also preferably, the fibrous sheet to form the backsheet is a water-decomposable nonwoven fabric having been subjected to water-jetting treatment, or it is water-decomposable paper.
Also preferably, the water-dispersible fibers are fibers of at least one selected from the group consisting of pulp, regenerated cellulose, abaca, and linter pulp.
Also preferably, the fibrous sheet to form the backsheet has a surface strength of at least 4 (in terms of wax number), measured according to JIS P8129-1976 2.1.